1. Field of the Invention
The present invention relates to a surface acoustic wave device for use in mobile communication equipment etc., and a manufacturing method therefor.
2. Description of the Related Art
The surface acoustic wave device has widely been used conventionally, as a duplexer and a filter for use in the mobile communication equipment etc.
As the prior art, FIG. 1 shows an exemplary configuration of the surface acoustic wave device described in Patent document 1.
In FIG. 1, there is shown a schematic configuration of the cross section of the surface acoustic wave device being individually cut out. A surface acoustic wave (SAW) device chip 1 is disposed on a circuit substrate 2, with each electrode for the formation of surface acoustic wave being placed on the upper side.
The electrode for the formation of surface acoustic wave disposed on SAW device chip 1 includes an interdigital transducer (IDT) 10 for exciting a surface acoustic wave and a pair of reflective electrodes 11 each disposed on each side of the IDT 10. The electrode is connected to an electrode 3 on the circuit substrate 2 side by means of a bonding wire 12 via a metal post.
Further, in the configuration shown in FIG. 1, SAW device chip 1 is covered with an insulating rim 4 and a lid 5, so that a hollow 13 is formed on a surface acoustic wave propagation path.
Now, in Patent document 1, as an effect of covering SAW device chip 1 with insulating rim 4 and lid 5, there is described that “because protection is made while a hollow (9) is maintained on the surface of a functional portion, stable manufacturing can be made without a risk of damaging a functional portion (1a) by mistake when the chip (1) is handled. Also, because the functional portion 1a is simply sealed with first and second insulating films 2a, 2b, it is not always necessary to tightly seal as in the conventional surface acoustic wave equipment. Thus, low-cost surface acoustic wave equipment is obtainable” (in the paragraph 0017 of Patent document 1).
In contrast, because the material forming the IDT and the reflective electrode is an aluminum alloy, it is known that the electrode becomes deteriorated because of eroded aluminum when being exposed in the atmosphere having high humidity in a long term (for example, lines 17-19 of page 1 in Patent document 2).
Specifically, FIG. 2 is a diagram illustrating the structure of a SAW device having the structure shown in Patent document 2. A connection electrode of SAW device chip 1 is connected to an electrode 3 on the circuit substrate 2 side through a metal ball 14. Thus, by means of metal ball 14, a hollow 13 is formed between SAW device chip 1 and circuit substrate 2.
Further, a resin cover 6 is formed on the upper face and the side faces of the SAW device chip 1. In order to prevent erosion of the electrode, with regard to the above resin cover 6, it is described that the resin cover 6 has to be formed of a resin having a small chlorine ion content.
[Patent document 1] Japanese Unexamined Patent Publication No. 2000-114918.
[Patent document 2] WIPO international publication No. WO 02/061943.
In the above Patent document 1, it is shown that photosensitive films are used for the insulating rim 4 and lid 5 (refer to FIG. 3 of Patent document 1). Further, it is obvious that the photosensitive film includes a halogen compound from the characteristic thereof, and in the manufacturing process of the SAW device, at the time of heating such as reflow, a portion of the halogen gas is emitted from the photosensitive film to the hollow (9)
Therefore, similarly to the case described in the aforementioned Patent document 2, there is a risk of bad influence such as erosion produced on the IDT, which is an electrode for the formation of surface acoustic wave disposed in the hollow, and the reflective electrode. However, in Patent document 1, there is neither disclosure nor suggestion about the influence on the electrodes caused by the halogen gas, not to mention the avoidance of the influence on such electrodes.
Meanwhile, as described above, the problem of an eroded electrode is shown in Patent document 2. As a method to solve the problem, it is disclosed that, through predetermined environmental processes (heating and pressing processes), a resin material of reduced chlorine ion content is to be used as a coating material.